The present invention relates to cardiac pacing generally and more particularly relates to cardiac pacing modes in which ventricular pacing pulses are delivered synchronized to sensed or paced atrial depolarizations.
The value of dual chamber cardiac pacing in treatment of patients suffering from hypertrophic cardiomyopathy has recently been recognized. The benefits of this therapy are discussed in the articles "Permanent Pacing as Treatment for Hypertrophic Cardiomyopathy" by Kenneth M. McDonald et al., published in the American Journal of Cardiology, Vol. 68, Jul. 1, 1991, pp. 108-110, "Impact of Dual Chamber Permanent Pacing in Patients with Obstructive Hypertrophic Cardiomyopathy with Symptoms Refractory to Verapamil and .beta.-Adrenergic Blocker Therapy" by Fananapazir et al., published in Circulation, Vol. 8, No. 6, June, 1992, pp. 2149-2161, "Effects of Dual-Chamber pacing in Hypertrophic Obstructive Cardiomyopathy", by Jeanrenaud, et al., published in The Lancet, Vol. 33, May 30, 1992, pp. 1318-1323, "Altered Cardiac Hemodynamic and Electrical State in Normal Sinus Rhythm After Chronic Dual-Chamber Pacing for Relief of Left Ventricular Outflow Obstruction in Hypertrophic Cardiomyopathy", by McAreavey et al., published in American Journal of Cardiology, 1992, Vol. 70, pp. 651-656 , and "Effects of Dual-Chamber Pacing in Hypertrophic Cardiomyopathy Without Obstruction", by Seidelin et al., published in The Lancet, 1992, pp. 340-369. In these papers, the value of DDD pacing employing a shortened A-V escape interval is discussed. In particular, the use of an A-V escape interval which is shorter than the patient's intrinsic A-V conduction is specifically recommended, with favorable results being reported so long as the duration of the pacemaker's A-V escape interval is not so short that hemodynamic performance is compromised. Various approaches to selecting the optimal A-V escape interval are discussed in the literature.
It is generally agreed that pre-excitation of the ventricular apex and septum by the ventricular pacing pulse, prior to excitation due to natural conduction between the atrium and ventricle is to be preferred. The abstract "How to Optimize Pacing Therapy in Patients with Hypertrophic Obstructive Cardiomyopathy: The Importance of AV Delay Programming" by Gras, et al., published in PACE, May, 1993, Vol. 16, Part II, page 1121 suggests that the longest A-V escape interval which provides complete ventricular capture should be selected. The above-cited article by Fananapazir suggests that the A-V escape interval which allows for maximal pre-excitation of the ventricle by the pacing pulse can be selected by employing the A-V escape interval that produces the widest paced QRS complex duration. The above-cited McDonald article suggests that the A-V escape interval should be set at the longest duration that maintains ventricular capture at maximum exercise levels.
In the abstract "The Optimal Patient for Pacemaker Treatment of Hypertrophic Obstructive Cardiomyopathy (HOCM) by Jeanrenaud et al, published in PACE, May, 1933, Vol. 16, Part II, page 1120, it is suggested that in the case of patients who would require an excessively short A-V escape interval in order to accomplish pre-excitation, intrinsic A-V conduction time could be prolonged by means of drugs or ablation techniques.